The present invention relates to coordinate reading devices which utilize magnetostrictive material as vibration transmission media.
Graphical data devices requiring position location are commonly employed in computer data input devices to constitute desired work force saving systems. In such devices, coordinate reading devices utilizing magnetostrictive vibration wave delay in magnetostrictive material, (such as shown in U.S. Pat. Nos. 3,846,580 and 3,904,821), are used widely because such devices are simple to construct and easy to operate.
Thus, a general explanation of a known such coordinate reading system is described below referring to FIG. 1.
The device shown in FIG. 1 consists of a tablet 1, a detector 2 having a pick-up coil and an input/output control 3 which is connected with the tablet 1 and the detector. The control 3 may be connected to an outside device 4 which may be any work force saving system.
To read the coordinates of a desired graphical pattern, (e.g. a circuit network, an electrocardiograph, an X-ray photograph or map), a pen or cursor type detector 2 traces the graphical pattern placed on the tablet 1. The tracing of the pattern forms analog data which is detected as X and Y axis deflections from a zero point, and the deflections are transformed into digital quantities of the input/output control 3 as X and Y coordinate data which is applied to a computer or printer.
As described, the device performs coordinate analysis in a one dimensional plane or in a two dimensional plane which measures X and Y axis deviation, utilizing a magnetostrictive vibration wave delay which is transmitted in a magnetostrictive material. In a two dimensional plane, tablet 1 has two magnetostrictive vibration transmission paths Lx and Ly which are vibrated by excitation coils Wx and Wy respectively to transmit X and Y axis vibration waves.
To form such magnetostriction vibration transmission paths Lx and Ly, rolled thin sheet or electroplated film separated from a base plate of electrostrictive material is cut into rectangles of the desired area. Exciting coils Wx and Wy are arranged at two edges of the rectangle respectively. In this case, no visible lines Lx and Ly are present.
Another method utilizes two such sheets, one for each of the X and Y axes, and forms many slits through the sheets by a photoetching process, to obtain substantial magnetostrictive vibration transmission lines Lx and Ly on each sheet. The sheets are layed together with an insulation sheet therebetween so that the slits are orthogonal to each other and the edges of the sheets are secured by a suitable adhesive material. The desired exciting coils Wx and Wy for the X and Y axis are applied to the sheets respectively. Some other tablets have rolled thin ribbon-shaped sheets, or rolled alloy wires.
In the above mentioned tablet 1, an exciting pulse current is applied to each exciting coil Wx and Wy to vibrate the magnetostrictive material sheet, to produce an excitation magnetic field which excites the sheet to produce a magnetostrictive vibration which is transmitted in the transmission path Lx and Ly to the other ends thereof. A detector 2 approaches a point P to be measured. Magnetic flux changes produced by the electrostrictive vibration which is propagated to the point P induce a voltage in the detector coil. Since the propagation delay time of the vibration wave corresponds to distance along the coordinate axis, the time difference between the detected time at point P and pulse current application time to the excitation coil is measured by counting clock pulses which can be used as coordinate values along an X or Y axis. The delay time is alternately read along X and Y axis. Any desired clock pulse generation and counting system may be used.
FIG. 2 shows the two dimensional tablet 1 as an actual device. Essential parts of the table 1, i.e., the above-mentioned vibration transmission media consisting of a magnetostrictive material must be magnetized to a suitable magnetic potential before reading operation. The magnetizing must be repeated with a predetermined period in relation to the frequency of the reading operation and time delay. Conventionally, a bar magnet 5 moves slowly from one corner diagonally as shown by arrow 6.
The magnetizing operation is performed before a series of reading. However, as the magnetizing function should be applied to the vibration transmission media in the tablet 1 uniformly and in a predetermined accurate direction, much skill is necessary to move the bar magnet so as to prevent the disturbing of an accurate coordinate reading operation. The moving speed of the bar magnet 5 also affects the reading accuracy of the tablet 1. Further, the distance from the surface of the bar magnet 5 to the tablet 1 also affects the reading accuracy. The difficult magnetizing operation must be repeated frequently whenever the exciting condition of the vibration transmission media is damped. As shown in FIG. 2, the effective reading area 11 is arranged within an outside casing 12 of the tablet 1.
When a magnetic disturbance is applied to the magnetostrictive material in the tablet 1, e.g., a disturbance caused by placing a magnet 7 on the tablet 1, the magnetizing effect of the tablet 1 is disturbed greatly, and the reading accuracy and reading function are also disturbed. Thus, after the magnet 7 is removed, the above-mentioned bar magnet magnetizing must be applied. Magnetic disturbance sources such as the magnet 7 are commonly present in stationery and business instruments so that care must be paid to prevent such a magnet from being placed near the tablet 1. When an operator does not know or notice that such a magnetic disturbance has been applied to the tablet 1, the coordinate readings which result are completely unreliable.